The widening use of packaging cases made of corrugated cardboard requires very high production rates. Present machines are capable of producing cases at a very high rate from a cardboard sheet representing the spreadout case to be obtained. At the present time, these machines are continuous machines in which the blank passes in succession from one station to the next, without any intermediate storage. In this way, the sheet is printed, cut out to form the turned-down portions or the auxiliary cut-out portions, glued on its closing tab, and then folded and bonded up to the final station for making up into bundles for delivery to the user.
In the folding part, the transverse end panels of the blank are folded inwards and bonded to one another. Folding is generally carried out by moving the cases along an endless conveyor (with belts, chains, etc.), the central part of the blank being retained firmly between the two folding lines of the latter, the end panels bearing on inclined bars which force them to lift up or descend, depending on whether folding takes place from above or from below. The end panels are thus arranged vertically, and they are, in general, subsequently picked up by other bars which complete the folding flat.
Instead of inclined bars, it is possible to use other devices, such as:
(a) straight or spiral movable belts which have the same function, PA1 (b) oscillating flaps which are driven in a cyclical movement and which push the panels at the rate at which they pass, until they are folded flat, PA1 (c) rotating spiral bars, such as those described in U.S. Pat. No. 4,254,692, the characteristic of which is to possess a single point of contact with a corresponding panel. PA1 (1) Use of endless conveyors of the conventional type, combined with the lightness of the sheets, means that the cases to be folded often do not pass through the folder in perfect synchronism with the general movement of the machine. This causes disturbances both in the operation of the folder and in that of the machine located immediately downstream of the latter. PA1 (2) The devices cause a relative movement, in the direction of travel, between the folding elements and the cases to be folded. This relative movement causes these cases to be braked, further aggravating the folding defects in the cycle of the cases. PA1 (3) Most of these folding elements act by bearing on the front part of the lateral panels, so that folding takes place slightly crosswise, and badly folded cases are obtained in the end. To overcome this last disadvantage, it has already been proposed, e.g., in German Patent Application No. 2,911,969, to use for auxiliary thrust movable elements driven by an endless chain, but this type of device requires a very complex mechanism which is incapable of allowing sufficient speed of advance to be obtained.
All these known devices have disadvantages, among them the following: